1. Field of the Invention
The present invention relates to a technique of improving the reliability of a semiconductor device. More specifically, the present invention relates to a semiconductor device including pad portions improved in structure, and to a manufacturing method thereof.
2. Description of the Related Art
In general, various semiconductor elements formed in a semiconductor substrate (Si wafer) are electrically connected via wires (metal wires). Known techniques for forming such metal wires include a technique by which, for example, grooves are formed by applying patterning and anisotropic etching to an insulation film formed on an Si wafer, and copper (Cu) used as a line material is then filled in the grooves. A metal wire formed by such a technique is generally called a “Cu damascene wire.”
Generally, the surface of the Cu damascene wire is apt to be oxidized. As such, for example, in the event of applying a bonding material onto a pad portion of the Cu damascene wire formed in a semiconductor element, when the surface of the Cu damascene wire is oxidized, the electric resistance is apt to rise at a contact between the pad portion and the bonding material. In addition, since Cu damascene wires are generally soft, when, for example, a needle of a probe used to perform electrical measurement is dropped onto a pad portion of the Cu damascene wire from an upper portion thereof, the needle can easily stick into the surface of the Cu damascene wire. Oxidation develops from a needle-stuck point, thereby causing the electric resistance to increase. To prevent the problem, aluminum (Al) wires are used to form top-layer wires onto Cu damascene wires. Generally, an Al wire has a higher oxidation resistance and hardness than Cu damascene wire. For these reasons, pad portions are formed of Al wires, not Cu damascene wires.
However, in a contact portion (connection portion) between a Cu damascene wire and an Al wire, Cu is apt to penetrate into Al. To prevent the problem, a barrier metal film (BM film) formed of a material having a high barrier property for preventing the penetration of Cu into Al needs to be provided between Cu damascene wires and Al wires. Generally, a barrier metal film between Cu damascene wires and Al wires is formed using TaN. Nevertheless, when the Cu damascene wire and the Al wires are connected to each other via the barrier metal film (TaN film) formed of TaN, connected portions therebetween tend to peel off from each other. A technique for preventing such inter-film peel is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 10-98039.